Problem Identifier / Cannabis Root Rot and Treatment

Cannabis Root Rot
Progressed root rot on a cannabis plant.

Root rot is a fungus that attacks the roots of plants. This occurs most frequently when the roots are weak due to insufficient nutrients, diseases or stress. Technically, root rot is a bacterial organism, often targeting seedlings and seeds first. Young plants are extremely vulnerable to rot. Root rot spreads extremely quickly due to rapid growth.

The rot spreads through spores too small to see with the human eye. These tiny spores begin by attacking one plant but can quickly destroy your entire crop if left untreated. There is no way to determine which part of your crop root rot will attack, but it is a threat to every type of growing medium. It spreads beneath the growing medium through water.

As the water moves through your root systems, the spores can travel to your entire crop. The spores germinate while moving, so once the next system of roots is reached, the spores have substantially multiplied. Once the spores have spread throughout your crop, immediate action is required to prevent a complete loss. There are numerous different organisms capable of causing root rot including parasitic oomycetes, algae, fungi and bacteria.

No matter which organism is responsible for the root rot, the signs will be similar but not identical. All different types of root rot are often referred to by growers as unhealthy root browning.

Cannabis Root Rot Symptoms

Cannabis Root Rot Symptoms
Symptoms of root rot on newly transplanted cannabis plants.

If you suspect your roots may be having an issue, look for the following root rot symptoms:

  • Unhealthy, drooping and curled or clawed leaves
  • Burnt leaf tips or edges
  • Brown, yellow or bronze stripes or spots
  • White or yellow coloration
  • Dropping and dying leaves
  • Appearance of nutrient deficiencies
  • Plants are absorbing less water

Root rot restricts your plant’s ability to draw oxygen, resulting in unhealthy, drooping, clawed or curled leaves. The leaf symptoms of cannabis root rot are extremely varied including burnt tips or edges, nutrient deficiencies, brown, bronze or yellow stripes or spots, and unusual symptoms within the leaves. Once the leaves have started to wilt, the coloration usually turns white or yellow.

The leaves will then start to die and fall off. These symptoms are the result of issues with the roots. Your roots will be unable to absorb nutrients or function correctly. In most instances, your plants will take in much less water. If your plant’s water absorption has changed and any of the other signs are present, you must take immediate action to get rid of the root rot or you will lose your crop.

What Does Cannabis Root Rot Look Like?

The most common cannabis root rot symptoms include:

  • Twisted, brown, slimy and unhealthy roots
  • Mushy and slimy roots
  • Roots are twisted together
  • Brown tinge on the roots
  • Substance on the roots with an appearance of snot
Cannabis Root Rot
The start of a root rot infection. With proper care and trimming of the diseased roots, this plant was saved.

Undesirable pathogens in a hydroponic tank can result in unhealthy, brown, slimy and twisted roots. Although no two infections appear exactly the same, the main symptom is generally brown roots. All of the roots can become infected, or only certain areas. The sections attacked usually become mushy and slimy, then begin to twist together. The appearance is similar to plants severely under or overwatered.

The part of the country you live in is important because such a wide variety of pathogens can cause root rot. The pathogens attacking plants in Maine will not be the same as those found in Arizona. The first stage of root rot is brown tinges appearing on the younger roots. Certain types of root rot will attack roots beneath the water surface, but the roots you see above the water will appear healthy and white.

This is the reason it is recommended you have a slight air gap beneath your net pots. Any moist environment rich in oxygen including a misty air gap makes the growth of root pathogens much more difficult. Look closely at the roots of your plants for a slimy or mushy appearance similar to snot. The roots become stuck together due to a lack of oxygen resulting in slime.

What Causes Cannabis Root Rot?

To help eliminate the potential causes of cannabis root rot, all of the following actions are recommended:

  • Do not disturb the roots
  • Change the reservoir
  • Do not allow the roots to sit in stagnant water
  • Avoid warm reservoirs
  • Eliminate light leaks in your reservoir
  • Make certain there is enough oxygen in the water
  • Maintain adequate oxygen levels
  • Immediately remove dead leaves or decaying matter in the reservoir
  • Do not overwater your plants

If you recently changed your reservoir or disturbed the roots of your plants, root rot is a distinct possibility. The risk increases if your plants are still young. Do not disturb the roots of your seedlings unless absolutely necessary. Roots need time for building up a biofilm critical for protection from root rot.

If your growing medium is either coco coir or soil, the number one cause of root rot is stagnant water. Undesirable organisms will thrive in old water obtaining light from any source including the sun. Allowing your plants to remain in this water is essentially an invitation for root rot because a breeding ground will develop enabling unwanted organisms to thrive.

If your reservoir is too warm, bacteria can reproduce a lot easier. The recommendation is to keep your reservoir cool to establish an environment where harmful fungi and bacteria are unable to survive. Look for light leaks in your reservoir. This will provide ideal conditions for smaller populations or destructive organisms. Make certain there is an adequate supply of oxygen in your water.

If you do not have adequate oxygen and/or air in the water of your reservoir, the result is an accumulation of organisms likely to cause root rot. Young roots require adequate oxygen to increase their defenses to diseases including rot. If you move your plants, not only will they become weaker, but you are potentially risking exposure to new pathogens. Check your reservoir for any decaying matter such as old leaves.

Any plant matter you see needs to be removed from your reservoir immediately. The only exception is the actual roots of your plants. Unless the roots are no longer attached to your plants, leave them alone. Root rot is the most common in cannabis plants grown in a hydro system. Another cause of pathogens resulting in rot is overwatering your plants in any growing medium including soil.

The best way to prevent root rot is to make certain your plants are not left in wet conditions for a long period of time with no oxygen.

How to Fix Cannabis Root Rot

How to Treat Cannabis Root Rot Indoors

Getting rid of root rot is difficult. For this reason, numerous growers prefer to get rid of their plants and start again. If this is the action you decide to take, it is critical to determine the cause of the rot if you are planting a new crop in the same area. If you do not identify and treat the cause prior to planting, your new crop will be attacked by root rot.

If you’re asking yourself, is root rot the end of my cannabis plant? The answer is not necessarily. There are techniques growers often use to cure their crops of root rot proven to be effective. Your first step is determining if your plants have been attacked by root rot. The next step is figuring out if you can still save your crop. If your entire root system has turned mushy, it is already too late.

Your only option is getting rid of your crop, treating the area and starting over. If you see any firm, white and healthy roots, there is a chance you can treat the root rot to restore the health of your plants. If you are growing your plants in soil, replace it with fresh soil containing all of the essential nutrients. Make certain your soil is draining well.

To regain health, nutrients must be available to the plant. Supplementing the roots provides plants with everything necessary to increase resistance levels to disease. Water with rich oxygen content is especially important for your plants. The idea is to make sure oxygen is dissolved within the water. If you are using a hydro system, you can accomplish this by purchasing an air pump of medium size and large air stones for your system.

The more surface agitation and bubbles you create the better because oxygen will easily dissolve within the water. As long as the oxygen is not disturbing the roots of your plant, there is no such thing as too much oxygen. Not only will your plants thrive, but they will also grow much quicker due to the higher oxygen level. For every ten gallons, you will need two outlets and one air pump.

Use standard 3/16th inch aquarium tubing to connect everything together. Look for black tubing since this will help prevent light from getting into your reservoir. In addition to your plant roots not liking the light, root rot thrives due to the light and heat generated by your grow lights. Plants grown in hydro require a pitch-black reservoir. Any light shining into the reservoir needs to be eliminated.

If you are unable to contain the light leaks, all of the options listed below are excellent to ensure no light penetrates.

Conduct a Thorough Check

Thoroughly inspect your reservoir for any light leaks. Getting down onto the floor to look upwards is a good way to spot any light.

Reservoir Tub

Give careful consideration to the thickness and material of your reservoir tub. If the material is thicker and darker, you will not need to be concerned about light reaching your reservoir.


Your tubing needs to be light-proof and dark to ensure your reservoir is protected from exposure to light. A good option is net pots with light-proofing. Pot inserts are available to enable you to fill your pot without the use of clay pebbles often resulting in light leaks. This will ensure the light is unable to penetrate your reservoir.


Always think about reflectivity. More light heat and light are reflected back if you choose a paler color. In a pinch, use reflective materials to cover your lid to stop the light.

Opaque Tape

You can cover any light by using opaque tape. The best options are reflective and electrical tape. Simply tape over the areas where light is penetrating into your reservoir.

Your growing medium temperature should be a maximum of 80 degrees Fahrenheit. For the best results, maintain a temperature of 75 degrees Fahrenheit. This will also decrease the water temperature within your reservoir. If your water temperature is too high, your plants will be unable to hold the desired level of dissolved oxygen. This means your plants will not be able to breathe correctly.

If the temperature of your growing space remains too high, your plants will begin to droop. The risk of root rot also increases significantly. A temperature of 72 degrees Fahrenheit is recommended for your reservoir water. In order to keep your reservoir this cool, you will need to plan ahead and use high-quality equipment for your growing medium.

If you are using a hydroponic setup, the water in your reservoir needs to be changed on a regular basis, and you need to carefully watch your plants’ roots. These steps are critical when your plants reach the flowering stage due to an increased sensitivity to pH and nutrients. Your water needs to be changed every seven to 10 days for two reasons. First, you will be helping to prevent toxicities and deficiencies. Secondly, you will be improving nutrient access.

The only exception is when you have first established either clones or young seedlings in a hydro system. The roots are too young for an established beneficial bacteria colony or biofilm. This means your roots are more susceptible to root rot. If you perform a complete reservoir change during this time, everything can be thrown off balance. This means the roots must essentially start the process all over again.

This is one of the key reasons growers struggle with root rot. Changing your reservoir during the first three to four weeks of the life of your plants is not recommended. Use nutrient water to top-off the water in your reservoir during this time. Wait until a healthy biofilm layer has developed, and covers the bottom and sides of your tank and the roots before completely changing your reservoir.

For a hydro system, check your reservoir regularly for any type of debris such as dead roots. This type of matter will begin to rot, offering an ideal breeding ground for root rot and numerous types of bacteria. By removing this matter immediately, you can keep your growing area clean. This will help prevent the growth of bacteria before it has a chance to start.

Prior to growing your plants, clean everything you will need to use to make certain any fungus or bacteria has been destroyed.

Treating cannabis root rot can be accomplished by using one or more of the following options.

  • Replanting in fresh soil
  • Ensure good drainage
  • Add beneficial bacteria and nutrients
  • Increase oxygen level in your water
  • Make certain your reservoir is pitch-black
  • Lower the temperature of your growing medium
  • Change your reservoir on a regular basis with the exception of clones
  • Clean out dead roots from your reservoir
  • Maintain a clean growing environment

How to Treat Cannabis Root Rot Outdoors

The best solution for outdoor root rot (and any pests, mold or mildews!) is prevention. You can stop the rot by filling in the areas of soil that are lower than the rest. Adding organic material will improve the quality of your soil and help improve drainage. If you are unable to improve drainage, use draining soil to fill raised beds. You can prevent overwatering by establishing a watering schedule.

Make certain your soil contains the essential nutrients and remains fairly dry. Your plants should not be irrigated until your soil is mostly dry. You can help with the evaporation of moisture from the soil by pulling it back. Rot thrives in excessively moist soil. Good options to treat outdoor root rot include:

  • Fill in lower areas
  • Add organic matter to your soil to ensure good drainage
  • Do not overwater your crop
  • Do not irrigate until your soil is nearly dry
  • Enable moisture evaporation by pulling back your soil

Washing Roots from Soil Cannabis Root Rot

If you notice symptoms of root rot during transplant, this would be the only time you may want to utilize a wash root technique to treat your plant. Cut away any dead roots with a clean pair of scissors, aerate the root ball, and use a beneficial bacteria such as bacillus during transplant.

How to Prevent Cannabis Root Rot

Prevent Cannabis Root Rot Indoors

You can prevent indoor root rot with the following options:

  • Verify the quality of your growing medium
  • Ensure adequate oxygen levels
  • Keep everything clean
  • Water your plants on a set schedule
  • Use a root booster
  • Ensure proper humidity and ventilation
  • Make certain your containers have adequate drainage holes
  • Use the correct sized container

Verify both the origin and quality of your growing medium. To make certain your plants have correct oxygenation, use a soil mix with good aeration. Your growing medium can never be too clean. Water your plants using a precise and strict schedule. You can enhance the health of your root system by using a root booster once per week. Keep a close eye on the humidity and ventilation to discourage root rot.

If the root rot has already reached the advanced stages, there is nothing you can do. You need to accept the loss of your crop, discard everything and start over again. Your growing room and tools will require a thorough cleaning. If you are growing your plant in a pot, make certain there are drainage holes in the bottom. Water must be able to get out of the pot or the roots can drown.

Do not use large containers for small plants or seedlings or the plant’s roots will have difficulty getting the right amount of oxygen. The plant must be large enough to partially fill up the pot. When you water, do so in a circle around the seedling, a little at a time until the growth rate has increased. Do not allow your plant to outgrow the container or it will become root bound.

If the roots of the plant are circling around the outside of the pot, your plant is root bound. Even if everything else you are doing is correct, your plant will have issues with nutrients and water absorption. You need to transplant your plant into a larger container to prevent the roots from choking your plant.

How to Prevent Cannabis Root Rot Outdoors

The best outdoor prevention options include:

  • Do not plant in muddy or thick soil
  • Use nutrient-rich soil with good drainage
  • Do not water your crop until the topsoil is dry
  • Immediately remove and discard affected sections of your plants

Only plant using fluffy and rich soil as opposed to thick or muddy. You need to be certain there is enough oxygen in the soil for supporting the roots.

Do not underestimate the importance of preventative pest control. Root rot is often carried by fungus gnats, so prevention is critical for healthy crops. Excess water will attract both root rot and fungus gnats.

Any affected areas of the plant or soil need to be removed and discarded immediately. This will help stop the spores from spreading to other plants and destroying your entire crop.

How Long Does it Take to Recover from Cannabis Root Rot?

Provided you have identified and treated the root rot correctly, your plants should recover in approximately five to seven days.

Defeat Pests, Mold and Mildew… NATURALLY!

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